1. Field of the Invention
The present invention relates to an organic light emitting display and a method of driving the same, and more particularly to an organic light emitting display and a method of driving the same, which compensates for the degradation of organic light emitting diodes.
2. Description of the Related Art
Recently, various flat panel displays capable of reducing weight and volume that are disadvantages of cathode ray tubes (CRTs) have been developed. Flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and organic light emitting displays.
Among the flat panel displays, the organic light emitting displays make use of organic light emitting diodes that emit light by re-combination of electrons and holes. The organic light emitting display has advantages of high response speed and low power consumption.
FIG. 1 is a circuit diagram showing a pixel of a conventional organic light emitting display.
With reference to FIG. 1, a pixel 4 of an organic light emitting display includes an organic light emitting diode OLED and a pixel circuit 2. The pixel circuit 2 is coupled to a data line Dm and a scan line Sn, and controls the organic light emitting diode OLED.
An anode electrode of the organic light emitting diode OLED is coupled to the pixel circuit 2, and a cathode electrode thereof is coupled to a second power source ELVSS. The organic light emitting diode OLED generates light of a luminance corresponding to an electric current from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 controls an amount of an electric current provided to the organic light emitting diode OLED corresponding to a data signal provided to the data line Dm. To do this, the pixel circuit 2 includes a first transistor M1, a second transistor M2, and a storage capacitor C. The second transistor M2 is coupled between a first power source ELVDD and the organic light emitting diode OLED. The first transistor M1 is coupled between the data line Dm and the scan line Sn. The storage capacitor C is coupled between a gate electrode and a first electrode of the second transistor M2.
A gate electrode of the first transistor M1 is coupled to the scan line Sn, and a first electrode of the first transistor M1 is coupled to the data line Dm. A second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor C. Here, the first electrode of the first transistor M1 is one of a source electrode or a drain electrode, and the second electrode is the other one of the source electrode or the drain electrode. For example, when the first electrode is the source electrode, the second electrode is the drain electrode. When a scan signal is supplied to the first transistor M1 coupled with the scan line Sn and the data line Dm, the first transistor M1 is turned on and provides a data signal from the data line Dm to the storage capacitor C. At this time, the storage capacitor C is charged with a voltage corresponding to the data signal.
A gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor C, and a first electrode of the second transistor M2 is coupled to another terminal of the storage capacitor C and a first power source ELVDD. Further, a second electrode of the second transistor M2 is coupled to an anode electrode of the organic light emitting diode OLED. The second transistor M2 controls an amount of an electric current flowing from the first power source ELVDD to a second power source ELVSS through the organic light emitting diode OLED according to the voltage charged in the storage capacitor C. At this time, the organic light emitting diode OLED emits light with a luminance corresponding to the amount of electric current supplied through the second transistor M2.
The pixel 4 of the organic light emitting display displays images of a desired luminance by repeating the aforementioned procedure. On the other hand, during a digital drive in which the second transistor M2 functions as a switch, a voltage of the first power source ELVDD and a voltage of the second power source ELVSS are supplied to the organic light emitting diode OLED. Accordingly, the organic light emitting diode OLED emits light with a regulated voltage drive. In the digital drive method, gradations of luminance, or gray levels are expressed using an emission time of the organic light emitting diode OLED while supplying a constant current to the organic light emitting diode OLED. However, in the digital drive method, because the organic light emitting diode OLED emits light with a regulated voltage drive, a degradation of the organic light emitting diode OLED progresses more quickly, with the eventual result that images of desired luminance cannot be displayed.
When the organic light emitting diode OLED degrades, resistance of the organic light emitting diode OLED increases. Accordingly, an electric current flowing to the organic light emitting diode OLED is reduced corresponding to the same voltage. This causes the luminance of images to be reduced.